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Conceptual Question: The Magnetic Field

  1. Feb 27, 2008 #1
    1. The problem statement, all variables and given/known data
    [​IMG]

    There are four wires viewed end-on in the drawing. They are long, straight, and perpendicular to the plane of the paper. Their cross sections lie at the corners of a square. Currents of the same magnitude are in each of these wires. Choose the direction of the current for each wire, so that when any single current is turned off, the total magnetic field at point P is directed towards corner of the square.


    2. Relevant equations



    3. The attempt at a solution
    I know that using the right hand rule by curling your fingers in the direction of the current you can find the direction of the magnetic field, but I don't think I am applying the rule right and I'm not sure how to get it so that if you turn a current off P always points to a corner. Can anybody help?
     
  2. jcsd
  3. Feb 27, 2008 #2

    Doc Al

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    Staff: Mentor

    Show what you've tried. For a given wire, which way does the magnetic field at P point? (Show how you are using the right hand rule.)

    Play around with it. The kinds of answers to consider are: Should the currents all point the same direction? Alternating directions? Etc... Just try various combinations until it works.
     
  4. Feb 27, 2008 #3
    Well I put the current going from wire 3 to wire 2 going up, wire 2 to wire1 going left, wire 1 to wire 4 going down, and wire 4 to wire 3 going right. Using the right hand rule if the current flow is stopped at either of the wires the way I used the rule it'll always face P, but I'm not sure if that is right.
     
  5. Feb 27, 2008 #4

    Doc Al

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    Staff: Mentor

    I believe you are misinterpreting the diagram. Those horizontal and vertical lines are not the wires. (They just mark off a square.) The wires (seen in cross-section only) are those four circles. The current goes into or out of the page.
     
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